The chief executive of Boeing has said the company was very close to getting its troubled 787 Dreamliner jet back into the skies.

The world's most advanced passenger plane has been grounded since January after battery fires on two of its jets. This week Boeing announced that it had completed the first successful test flights after making changes to its lithium-ion battery systems.

"We have a high degree of confidence in the technical solution we are testing right now with the Federal Aviation Administration," said Jim McNerney. "I think it will be sooner than later."

He expected the tests to conclude in a few days and said the data should be conclusive enough to persuade regulators to let the plane fly again.

He called the grounding a "frustrating experience" but said regulators were putting safety first. "They have the best interest of the flying public in mind," McNerney said.

Boeing is believed to be testing a new casing for the batteries and a venting system to disperse potentially flammable gases. The Dreamliner has been built with a radical carbon-fibre structure designed to make the plane as light as possible, generating savings on fuel that have made the jet an attractive proposition to customers such as Thomson Airways in the UK.

The first serious incident to affect the plane saw a 787 battery burst into flames on 7 January while it was parked at Logan airport in Boston.

The second incident took place on 16 January when a battery triggered a smoke alarm while in flight in Japan.

Investigators in Tokyo and the US have yet to identify a definitive cause of the fires, although the National Transport Safety Board has singled out short circuits across the battery's eight cells as a possible cause.